147 
which kept them expanded. The nets or webs were bluish green 
in colour on account of the blue green algæ caught in them. 
Dr. Wesenberg-Lund has informed me, that the colour of the 
nets altered with the seasons and was dependent on the colour of 
the plankton. In early spring, when diatoms were very abundant, 
the nets were brown or yellowish brown; in summer, when the 
blue-green algæ were predominant, the colour was bluish green. 
The nets were not in any definite order. 
x g kk 
In the vicinity of Silkeborg, in a small rivulet, Faarbæk, I 
found the catching-net made by the larva of Polycentropus flavo- 
maculatus Pict. These nets were found singly on the bottom, 
which was composed of fine-grained sand. It was only where there 
was a small stone, to which one of the fore corners of the net 
could be fixed that one or two nets were found. Fig. 4 represents 
a net on the bottom of the stream. The net resembles much the 
nest of Hirundo rustica. Along the one bank of the stream, con- 
sisting of a clayey or peaty soil, there were numbers of similar 
nets, just from the surface of the water down to the bottom. 
These nets were placed quite irregularly. Fig. 5 represents a small 
part of the bank. All the nets were bluish green in colour. The 
larva was always situated at the bottom of the net. 
The depth of the water in the four localities was ca. 15 cm. 
I have not visited the locality Filsø in Jutland, but Dr. 
Wesenberg-Lund informs me that the nets there were longer, 
the mouths wider and the tubes narrower. 
5 x år É 
The webs are assuredly to be considered as catching nets. 
The larva remains at the bottom of the web and captures the food, 
which the flowing water brings along. The nutriment of the larvæ 
is mainly plankton daphnids, remains of which are found in great 
multitude in their digestive organs. 
